Specializations/Generalizations

Use

The aim of the concept of specializations and generalizations is to allow the subdivision of entity types into subtypes. There are a number of different categories of specialization. The specialization category determines the criterion for the specialization. Specializations are linked to the source entity type (=generalization) via the specialization category.

Example

Generalization, specialization category, specialization

Term	Example
Generalization	People at the university
Specialization category	Activity
Specializations	Students, professors, administrative staff, research assistants

The generalization contains the attributes that are common to all entities of an entity type. These attributes are inherited by the specializations (more information: Attributes of Entity Types) and may be supplemented by other specific attributes.

The specialization category can be characterized by the attributes:

Complete:

Each entity of the generalization occurs at least once in a specialization of the category.
Disjunct:

Each entity of the generalization occurs in a maximum of one specialization of the category.

Example

The specialization category Activity is complete in the university example, since each university member belongs to at least one specialization. This specialization category is not disjunct, however, since it is conceivable that a person might be at the same time both a student and a research assistant with the result that they would occur in both specializations.

Note

A specialization category does not need to be either complete or disjunct.

More Information

Data Modeler: Overview

Entity Types

Attributes of Entity Types

Relationships

Structural Concept: Data Model and Data Model Hierarchy

Top-Down and Bottom-Up Modeling

Consistency Checks